Zein is a group of plant proteins that can be extracted from corn or corn-protein-containing substrates, such as corn gluten meal. Zein is classified as GRAS (Generally Recognized As Safe) by the U.S. Food and Drug Administration and has a variety of commercial uses including the manufacture of edible food packaging, edible films, biodegradable plastic resins, chewing gum base, tablet-coating compounds, adhesives, coatings for paper cups, soda bottle cap linings, etc. Zein can also be processed into resins and other bioplastic polymers, which can be extruded or rolled into a variety of plastic products. Zein has utility as a raw material for a variety of non-toxic and renewable polymer applications.
Zein belongs to a class of proteins called prolamins, soluble in alcohol. Zein comprises approximately forty to fifty percent of the total protein in corn, or about four percent of the corn kernel. Zein has been further divided into four subclasses: alpha-zein, beta-zein, gamma-zein, and delta-zein. Alpha-zein is the primary commercially used zein and accounts for about seventy percent of the zein in corn. Beta-zein accounts for about five percent of zein in corn. Gamma-zein accounts for approximately twenty to twenty-five percent of zein in corn and delta-zein accounts for about one to five percent of zein. Each zein type (alpha, beta, gamma, and delta) has a different amino-acid profiles and exhibits slightly different properties. Zein can be extracted and recovered from corn or co-products from corn processing.
Corn gluten meal, a by-product of ethanol production by wet milling, is a typical starting material for zein extraction because its protein content is sixty percent or greater. Sulfur dioxide or other chemicals that may be used during the preparation (e.g., in a steeping process) of corn gluten meal may adversely affect zein quality.
Ethanol can be produced from grain-based feedstocks (such as corn), cellulosic feedstocks (such as switchgrass or corn cobs), or other plant material (such as sugar cane). Ethanol production from corn produces fermentation products (e.g., co-products) that are suitable for use as starting materials for zein extraction.
In a wet milling process ethanol is produced from corn by first steeping the corn kernels in water that contains sulfur dioxide, and then separating the kernels into endosperm, fiber and germ. The endosperm is further processed to produce starch and corn gluten, which can be dried into corn gluten meal. Corn gluten meal may comprise at least sixty percent protein, and is typically used as a starting material for zein extraction in commercial zein production. The sulfur dioxide or other chemicals that may be used during the preparation of corn gluten meal may adversely affect zein quality.
Ethanol can also be produced from corn using a dry-milling process. In a dry-milling process, a starch containing material, such as corn, is ground into flour and is slurried with water and enzymes. The slurry may be cooked to liquefy the starch and to facilitate saccharification. Additional enzymes may be added to complete saccharification to break down the starch into simple sugars (e.g. glucose) that can be fermented using an ethanologen (e.g. yeast). The fermentation produces a fermentation product that comprises a liquid portion or component and a solids portion or component. The liquid portion comprises ethanol and water and soluble components. The residual solids comprise for example proteins, fiber, oil, and other insoluble components.
The fermentation product comprising a liquid component and a solids component may be distilled to separate ethanol and whole stillage (e.g. wet solids or fermentation solids). Whole stillage comprises residual solids and water, and may be further separated into wet cake and thin stillage. Wet cake (wet solids) can be dried into meal such as dried distillers grains (DDG); thin stillage can be reduced to syrup and added to the wet cake or meal during the drying process to produce dried distillers grains with solubles (DDGS). Meal such as DDG and DDGS can be used as an animal feed product
According to an alternative process, for example as described in U.S. Patent Application Publication No. 2005/0239181, starch may be converted into sugars and fermented in a raw-starch process without “cooking” or liquefaction. Heat damage to proteins and other components of the slurry may be avoided by using the raw-starch process.
A dry fractionation process that does not utilize sulfur dioxide may be used instead of wet milling to fractionate the corn into endosperm, fiber and germ. The amount of residual solids in the fermentation product can be reduced by fractionation and by eliminating fiber and germ, both low in starch, from fermentation. Endosperm is primarily comprised of starch and protein with small amounts of fiber and oil present. Zein is also concentrated in the endosperm; more than half of the endosperm protein may be comprised of zein. When endosperm is fermented, the residual solids comprise a high concentration of zein. The dried residual solids from endosperm fermentation are high in protein and result in a meal that is called “high protein dried distiller grains” (DDG HP).
Distillers dried grains (DDG) contain zein, but a high percentage or high quality of zein may not be recovered, if the product has been subject to chemical treatments or heat.
It would be advantageous to provide for a system for extracting protein from a fermentation product. It would also be advantageous to provide for a method of producing bioproducts from a feedstock in a system configured to produce ethanol and distillers grains from a fermentation product. It would also be advantageous to provide for a system configured to process feedstock into a fermentation product and bioproducts including ethanol and meal. It would also be advantageous to provide for a bioproduct produced from a fermentation product produced from a feedstock in a biorefining system.